The screw goes in and out but has no impact on idle speed. It's not idling very well and with the rekluse in there the bike is stalling on downhills.

Get another idle screw and try that first. Over time they wear out and the bike won't idle. It's a common problem on all modern 2 stroke 125 and 250s. Many manufacturers included a plastic idle screw instead of metal. (KTM) Some used aluminum. I wanna say Yamaha used a steel screw and they hold up better. But either way they all eventually need to be replaced.